"In the case of the Affordable Care Act, CBO has done important analysis and probably will continue to look at it. I think they've recognized that the impact of the act is likely to be complex," Yellen told members of the House Financial Services Committee on Tuesday. "I think they're still attempting to figure out what all of the different channels are by which it will affect the economy."

Obamacare's impact on jobs has been the subject of intense debate in Washington over the past week. Wonks, lawmakers, and pundits sparred over a report from the nonpartisan CBO last week that said the health reform law would reduce employment by the equivalent of 2.5 million full-time workers in 2024.

The CBO's report made such a splash because when the office last looked at the labor market impact of the Affordable Care Act, it estimated that the number of hours worked would be reduced by the equivalent of 800,000 workers in 2021.

In the report, the budget office said the new estimate—2.3 million in 2021—was the result of the incorporation of "additional channels" into its estimate. Yellen said CBO is likely to continue looking into these channels.

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She was appearing before the Financial Services Committee on Tuesday to deliver congressionally mandated semiannual testimony.